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At least 19 recordsLinked to original sources
PubMed2000

Multiple imputation compared with some informative dropout procedures in the estimation and comparison of rates of change in longitudinal clinical trials with dropouts.

Statistical analysis based on multiple imputation (MI) of missing data when analyzing data with missing observations is gaining popularity among statisticians because of availability of computing softwares; it might be tempting to use MI whenever data is missing. An important assumption behind MI is the "ignorability of missingness." In this paper, we demonstrate the use of MI in conjunction with random effects models and several other methods that are devised to handle nonignorable missingness (informative dropouts). We then compare the results to assess sensitivity to underlying assumptions. Our focus is primarily to estimate and compare rates of change (of a primary variable). The application dataset has a high dropout rate and has features to suggest informativeness of the dropout process. The estimates obtained under random effects modeling with multiple imputation were found to differ substantially from those obtained by methods devised to handle informative dropouts.

Algorithms↗
PubMed1979

Are dropouts, dropouts?

In this study, the perceptions of unilateral terminators, "dropouts," of their visit to a community mental health center were examined. A telephone survey was conducted to assess client satisfaction, impressions of the setting and therapist, helpfulness of the visit, expectations of and reported services received, and source and degree of problem(s) solution. Forty-seven respondents participated in the survey. Seventy percent were satisfied with the service they received. Satisfaction was related to favorable perceptions of the setting, the therapist, helpfulness of the visit, and whether improvement was due to contact with the center. Almost 80% of the respondents reported their problems had improved. Expectations of services to be rendered were generally met. Meeting of expectations was related to client satisfaction and perceived helpfulness but not to problem solution. Center impact was related to client satisfaction, mode of entry, meeting of clients' expectations, and number of services received. The study suggests that unilateral client termination is not a failure of the client or the intervention system. Clients can benefit from one session, use alternative sources of assistance, or be affected by environmental changes.

Community Mental Health Centers↗
PubMed2000

Attrition in an exercise intervention: a comparison of early and later dropouts.

OBJECTIVE: To identify reasons for dropout and factors that may predict dropout from an exercise intervention aimed at improving physical function in frail older persons. DESIGN/SETTING: An 18-month randomized controlled intervention in a community setting. The intervention comprised 2 groups: class-based and self-paced exercise. PARTICIPANTS: 155 community-dwelling older persons, mean age 77.4, with mildly to moderately compromised mobility. MEASUREMENTS: The primary outcome measure was dropout. Dropouts were grouped as: D0, dropout between baseline and 3-month assessment, and D3, dropout after 3-month assessment. MEASUREMENTS: Measurements of demographics, health, and physical performance included self-rated health, SF-36, disease burden, adverse events, PPT-8, MacArthur battery, 6-minute walk, and gait velocity. RESULTS: There were 56 dropouts (36%), 31 in first 3 months. Compared with retained subjects (R), the D0 group had greater disease burden (P = .011), worse self-perceived physical health (P = .014), slower usual gait speed (P = .001), and walked a shorter distance over 6 minutes (P<.001). No differences were found between R and D3. Multinomial logistic regression showed 6-minute walk (P<.001) and usual gait velocity (P<.001) were the strongest independent predictors of dropout. Controlling for all other variables, adverse events after randomization and 6-minute walk distance were the strongest independent predictors of dropout, and self-paced exercise assignment increased the risk of dropout. CONCLUSIONS: We observed baseline differences between early dropouts and retained subjects in disease burden, physical function, and endurance, suggesting that these factors at baseline may predict dropout. Improved understanding of factors that lead to and predict dropout could allow researchers to identify subjects at risk of dropout before randomization. Assigning targeted retention techniques in accordance with these factors could result in decreased attrition in future studies. Therefore, the results of selective attrition of frailer subjects, such as decreased heterogeneity, restricted generalizability of study findings, and limited understanding of exercise effects in this population, would be avoided.

Activities of Daily Living↗
PubMedDate not supplied

Mexican American and white American school dropouts' drug use, health status, and involvement in violence.

A group of Mexican American and white American school dropouts were compared with a control group and a group of academically at-risk students in three locations in the Southwest. The sample group consisted of school dropouts and comparison subjects in grades 6 through 12. Both comparison groups were matched with the dropouts by sex, ethnicity, and school grade. At risk students also were matched by age and grade point average. Dropout subjects were found to have the highest rates of alcohol and drug use, followed by at risk student subjects. The relative rates of use were about the same for nearly all drugs, with the largest differences found for drinking to intoxication and use of marijuana, uppers, and cocaine. Among the dropouts, 75 percent of Mexican American males and 90 percent of white American males had tried marijuana. More than a third of the dropouts had tried cocaine. One-third of the Mexican American males and more than half of the females in both the Mexican American and the white American group had tried uppers. Females, especially dropouts, had higher rates of tobacco smoking than males. The rates of cigarette smoking among dropouts were significantly greater than among the control group only for males. Health problems of parents were not related to dropping out of school for any of the ethnic or sex groups. However, dropouts were more likely to have had serious illness within the preceding year than members of the control group. Many dropouts live in a violent and dangerous world. As an example, about one in five dropouts had held a gun on someone in a confrontation, and 20 percent had cut someone with a knife. Nearly half had been badly beaten. Females were rarely perpetrators of crimes or misdemeanors, but were often victims. Forty-two percent of the white American female dropouts had been either raped or sexually assaulted. Mexican American females were found less likely to be victims of violence, which perhaps reflects cultural values of marianisma and machismo, involving protectiveness toward females.

Achievement↗
PubMed1999

Relating speech and swallow function to dropout in a longitudinal study of head and neck cancer.

The relation between functional outcome and dropout from a 12-month follow-up period was examined in a longitudinal study whose objective was to define and quantify the functional effects of oral surgical resection and reconstruction on speech and swallowing in patients with head and neck cancer. In a group of 150 patients recruited to a surgical study in the Cancer Control Science Program in Head and Neck Cancer Rehabilitation, dropout from all causes and dropout from specific causes (medical, patient, and administrative specific) were assessed in relation to longitudinal speech and swallow function. In univariate analysis, better speech articulation was associated with decreased risk of dropout from all causes and from medical-specific causes. Better swallow performance was associated with decreased risk of medical-specific dropout. Multivariate analysis revealed the following: (1) only articulation function was associated with dropout from all causes; (2) the association of speech articulation function with medical dropout was diminished after adjusting for advanced age and surgical resection variables; (3) the association of speech articulation function became significant for patient-specific dropout after adjusting for advanced age and surgical resection variables and indicated that better function decreased the risk of this type of dropout; and (4) swallowing function was not related to dropout. Patients treated for oral or oropharyngeal cancer who have poorer speech outcomes are more likely to drop out from a longitudinal study. Basing study results on only patients who complete a longitudinal study will understate the level of dysfunction experienced.

Adult↗
PubMed2002

Liver transplantation for hepatocellular carcinoma: analysis of survival according to the intention-to-treat principle and dropout from the waiting list.

A major obstacle for orthotopic liver transplantation (OLT) as treatment for hepatocellular carcinoma (HCC) is tumor growth resulting in dropout from the waiting list for OLT. There is a paucity of data on survival according to intention-to-treat analysis and the rate of dropout from the waiting list for OLT among patients with HCC. To further evaluate these issues, we analyzed the outcome of 46 consecutive patients with HCC listed for OLT between January 1998 and January 2001. Exclusion criteria for OLT were tumor size greater than 5 cm for one to three lesions or four lesions or greater of any size. Twenty-one patients underwent OLT. There were 11 dropouts because of tumor progression and six deaths, including three deaths after dropout. Kaplan-Meier 1- and 2-year intention-to-treat survival rates were 91.7% and 72.6%, respectively. Monthly dropout rates were 0% from 0 to 3 months, 1.5% from 3 to 6 months, 1.0% from 6 to 9 months, 4.9% from 9 to 12 months, and 5.6% from 12 to 15 months. One dropout occurred beyond 15 months among 4 patients remaining at risk. Cumulative probabilities for dropout at 6, 12, and 24 months were 7.3%, 25.3%, and 43.6%, respectively. Predictors for dropout included two or three tumor nodules or a solitary lesion greater than 3 cm at initial presentation and previous hepatic resection. Our results support recent changes in the scheme of organ allocation aimed at reducing the dropout rate and improving outcome for patients with HCC awaiting OLT.

Carcinoma, Hepatocellular↗
PubMed2000

Logistic regression and survival analysis of 450 impotent patients treated with injection therapy: long-term dropout parameters.

PURPOSE: We report the dropout rate associated with intracavernosal self-injection for erectile dysfunction at long-term followup, and determine parameters related to dropout. MATERIALS AND METHODS: Of 2,252 impotent patients evaluated during 9 years 450 (20%) enrolled in our self-injection program. Papaverine and phentolamine were given in 53% (initial treatment), prostaglandin E1 in 21%, and papaverine, phentolamine and prostaglandin E1 (triple mixture) in 26% of cases. Average injection volume for the 3 injection types was 0.52 cc. Data were retrospectively reviewed for patient dropout versus nondropout, specifically for type of drug, volume injected, changing treatment (from 1 drug and/or dosage to another), patient age, marital status, ethnic group, impotence duration and diabetes. RESULTS: Patient age ranged from 23 to 79 years (mean age 55). Of the patients treated at least 4 months 155 (35%) dropped out of the study. Mean treatment duration was 3.5 years. Logistic regression suggested that type of drug, changing treatment during the course of therapy and dosage (volume injected) were the only significant (p <0.05) parameters influencing dropout. Papaverine and phentolamine were twice as likely to lead to dropout as triple mixture or prostaglandin E1, and injection greater than 0.5 cc was more than twice as likely to lead to dropout. Demographic, ethnic, age and etiological factors had no significant effect on the overall dropout rate. CONCLUSIONS: The effectiveness of injection therapy was an underlying factor determining the long-term dropout rate for patients with erectile dysfunction. Other parameters or combinations of parameters that may influence patient dropout remain to be explored.

Erectile Dysfunction↗
PubMed2001

Children with persistent conduct problems who dropout of treatment.

Dropout of treatment is one of the key issues in outcome in a child and adolescent mental health service. We report two studies focusing on the treatment process and the dropout rate of children with persistent conduct problems presenting to a community mental health service, using a prospective design. The first study included 32 children and used a randomised controlled treatment design comparing a CBT approach with conjoint family therapy and an eclectic approach. The overall dropout rate was 36%. Dropout occurred significantly less frequently in the CBT group. The dropout group was associated with mothers who were younger and less educated, a poorer rating by the clinicians at the last meeting, parental dissatisfaction with the treatment service and perception that the treatment was less organised and having less behavioural tasks. In the second study we used a naturalistic follow-up design. Forty-six children were included. The overall dropout rate was 48%. Again, the children who defaulted were rated by clinicians as less likely to have improved and dropout was also significantly associated with parental perception of a less organised treatment. In both studies dropout usually occurred after assessment and at the early phase of treatment.

Adolescent↗
PubMed2003

A follow-up analysis of the pattern and predictors of dropout from the waiting list for liver transplantation in patients with hepatocellular carcinoma: implications for the current organ allocation policy.

Since our interim report of the intention-to-treat outcome of orthotopic liver transplantation (OLT) for hepatocellular carcinoma (HCC), we have performed a follow-up analysis of an expanded cohort of 70 patients to further assess whether the observed pattern and predictors of dropout are consistent with the rationale behind current HCC-adjusted Model for End Stage Liver Disease (MELD) organ allocation scheme. All except one patient had pretransplantation staging meeting our proposed expanded criteria-a single lesion < or =6.5 cm, or three or fewer lesions none >4.5 cm and total tumor diameter < or =8 cm. Thirty-eight patients received OLT. The cumulative probabilities of dropout at 6, 12, and 18 months were 7.2%, 37.8%, and 55.1%, respectively. The respective dropout probabilities would have been 11.0%, 57.4%, and 68.7% if the United Network for Organ Sharing (UNOS) criteria for exclusion (single lesion < or =5 cm or three or fewer lesions none >3 cm) were applied. Predictors of dropout with either criteria included three tumor nodules and a single lesion >3 cm at initial presentation, whereas preoperative chemoembolization or ablation therapies were associated with a lower risk for dropout only when applying the UNOS criteria for patient exclusion. In the subgroup with two or three lesions or a solitary tumor >3 cm, the cumulative probabilities of dropout were nine-fold higher than those with a single lesion < or =3 cm (P =.004). In conclusion, the low dropout rate in the first 6 months and the differing dropout risks based on tumor characteristics support further refinements in the HCC-adjusted MELD organ allocation scheme.

Adult↗
PubMed2003

Reduced burden of disease and improved outcome of patients with rheumatoid factor positive rheumatoid arthritis compared with dropouts. A 10 year observational study.

Our objective was to determine outcome and burden of disease in a 10 year study of patients with rheumatoid factor positive rheumatoid arthritis (RF+ RA) compared with study dropouts. Three hundred and one consecutive subjects with disease duration of 3-255 months at presentation were enrolled. The acute (as measured by C-reactive protein, CRP) and chronic (by erythrocyte sedimentation rate, ESR) phases of RF+ RA were suppressed by pulse intravenous (IV) combination of low dose methylprednisolone (MPS) + cyclophosphamide (CYC) for 3 consecutive days and weekly intravenous methotrexate (MTX) with simultaneous oral cyclosporine (CSA) + mycophenolate mofetil (MPM). After achieving negative CRP and ESR < 40 mm/h, IV therapy was tapered and switched to oral low dose MTX+CSA+MPM until negative CRP titer and ESR < 25 mm/h (men < 15 mm) Westergren were achieved. American Rheumatism Association (ARA) functional classification measured disability. Dropouts did not complete the study for various reasons. At baseline, cases and dropouts were comparable in age and sex distribution, including mean age, disease duration, disease features, and associated conditions. Mortality in 274 cases was 2.9% versus 25.9% in dropouts. ARA functional class in cases decreased from 3.2 + 0.7 to 1.4 + 0.3 and in dropouts was 3.2 + 0.6 at baseline versus 3.5 + 0.5 at outcome. Disability of dropouts was significantly worse compared with cases. In dropouts, more associated conditions occurred than in cases. The burden of disease and outcomes were significantly worse in dropouts compared with cases.

Adolescent↗
PubMed1997

A median-based test under informative dropout: the one-sample case.

We consider a clinical trial in which the outcome can be assessed by a continuous measure and where dropouts tend to have poorer efficacy than completers. When each subject can act as his/her own control, efficacy is measured by the difference between the outcome measurements at two times. When all subjects complete the protocol, a paired t-test can be used to test for a treatment effect, i.e., whether or not the mean difference is zero. When a patient does not return for the final evaluation, a measure of efficacy cannot be computed for that subject. Often, data from dropouts are ignored and only the observed pairs are used to analyze the data. When the reason for dropping out is not random, the result may be misleading. In this paper, we assume that (1) the distribution of the measure of efficacy (i.e., the change between two outcome measurements) is Gaussian, (2) dropouts would have worse efficacy than the median if they were observed, and (3) the dropout rate is less than 50%. We propose a median-based t-like statistic using the sample median in place of the sample mean. The variance of the median is estimated using only data from the complete half-sample, i.e., the half-sample with better efficacy. Simulations under five patterns of dropouts are performed to compare the proposed statistic with the paired t-test. The results show that the median-based statistic provides a conservative bound for the test of significance of the treatment. In contrast, because the paired t-test does not preserve its level of significance, except when the dropout mechanism is uniform, the paired t-test should not be used for trials in which dropouts tend to have poorer efficacy than completers.

Bias↗
PubMed2003

A joint model for nonlinear longitudinal data with informative dropout.

Subject withdrawal from a study (also called dropout, or right censoring), is common in late phase clinical trials. A number of methods dealing with dropouts have been used in practice, the most common being "last observation carried forward" (LOCF). Many of these methods, including LOCF, can result in biased estimates of the efficacy or potency of the drug, especially in the modeling context. If the likelihood of dropout is correlated to the underlying unobserved data, the dropout is informative and should not be ignored in the modeling process. The topic of informative dropout in the context of longitudinal data has received much attention in the statistical literature, in the setting of linear and generalized linear models. We extend the approach to nonlinear models. The dropout hazard, as well as the longitudinal data, is modeled parametrically. Parameters are estimated by maximizing the approximate joint likelihood as implemented in the software NONMEM. Using data from actual clinical trials, we explore the impact of the dropout model on the ability of the joint model to predict observed longitudinal data patterns.

Clinical Trials as Topic↗
PubMed2000

The association between severity of sanction imposed for violation of tobacco policy and high school dropout rates.

This investigation explored the association between severity of sanctions imposed on students resulting from tobacco policy violation and the event dropout rate in South Carolina public high schools. The study employed a cross-sectional design (n = 132). Surveys were mailed to school principals to assess tobacco policy and sanctions for violation. Severe sanctions were categorized as those resulting in the student being denied onsite instruction, such as out-of-school suspension or expulsion. General linear regression models adjusting for SES, ethnicity, and rural/urban status, tested for an association between event dropout rate and severity of sanction imposed. The mean dropout rate in 1998 for high schools in South Carolina was 2.58% (+1.74). Suspension at first violation and expulsion were associated with lower dropout rates. Suspension at second violation was not associated with dropout behavior while suspension at third violation was associated with higher dropout rates. Results from the study provide preliminary evidence that severe sanctions imposed for violation of tobacco policy may help reduce high school dropout rates.

Adolescent↗
PubMed1997

The effect of school dropout rates on estimates of adolescent substance use among three racial/ethnic groups.

OBJECTIVES: This study examined, across three racial/ethnic groups, how the inclusion of data on drug use of dropouts can alter estimates of adolescent drug use rates. METHODS: Self-report rates of lifetime prevalence and use in the previous 30 days were obtained from Mexican American, White non-Hispanic, and Native American student (n = 738) and dropouts (n = 774). Rates for the age cohort (students and dropouts) were estimated with a weighted correction formula. RESULTS: Rates of use reported by dropouts were 1.2 to 6.4 times higher than those reported by students. Corrected rates resulted in changes in relative rates of use by different ethnic groups. CONCLUSIONS: When only in-school data are available, errors in estimating drug use among groups with high rates of school dropout can be substantial. Correction of student-based data to include drug use of dropouts leads to important changes in estimated levels of drug use and alters estimates of the relative rates of use for racial/ethnic minority groups with high dropout rates.

Adolescent↗
PubMed1999

The causes of patient dropout from penile self-injection therapy for impotence.

PURPOSE: Penile self-injection therapy, a second line treatment for erectile dysfunction, is the most efficacious means of reestablishing functional erections when first line therapies fail and the patient wants to avoid penile prosthesis implantation. Despite high efficacy rates, injection therapy has high dropout rates. To our knowledge studies to date analyzing patient attrition have reviewed small numbers of patients followed for only short periods. We elucidate the main reasons for patient dropout in a large penile self-injection program with long-term followup. MATERIALS AND METHODS: A questionnaire was mailed to 1,424 patients who completed the office training and home use phases of a penile self-injection program. RESULTS: The overall attrition rate was 31% of the 720 men who completed the questionnaire, with a mean followup of 38 months. The main reasons for dropout were cost of therapy, patient and partner problems with the concept of penile injection, lack of partner availability and spontaneous improvement in erections. Lack of efficacy of therapy was the primary reason for only 1 of 7 dropouts. Furthermore, adverse effects of penile injections (priapism, penile nodules, pain) appeared to be only minor contributors to dropout. CONCLUSIONS: To our knowledge this study is the largest published, single center cohort of patients treated with injection and followed for an analysis of dropout rates. Based on study data a reduction in dropout rates may be achieved by keeping the cost of therapy low, and ensuring patient and partner education as well as continued support throughout treatment.

Adult↗
PubMedDate not supplied

Dropouts during treatment for leprosy (a study in the ELEP leprosy control project, Dharmapuri district, Tamilnadu during 1975-77).

Certain Social and Related Factors responsible for 231 dropout leprosy patients from treatment are discussed. Dropout rate was lowest among lepromatous patients (1.2% Vs 10.9% among nonlepromatous patients); patients with stigma/deformity were significantly less (P less than .001); among dropouts; proportion of wage-earners was high in them (p less than .001); student dropouts were few (Z-2.78, P less than .05, X2 - 10.32, d.f.-1, P less than .005); there was little association between socioeconomic status and dropout rate (P greater than .5); dropouts amongst patients who self-registered for treatment were much less than in those who were enlisted for treatment during survey (P less than .05); 38% had dropped out within the first six months of registration for treatment; lepromatous patients attended clinics for more than 25 months before becoming dropouts; fear of loss of wages, belief that it was not leprosy, social stigma attached to the disease, disinterest for treatment when lesions were small and few, dissatisfaction with treatment, and belief that patches self-healed were the main causes for discontinuance of treatment; all those who dropped out due to shyness were women of 15-44 age-group.

Adolescent↗
PubMed1978

Multiple predictors of dropout from alcoholism treatment.

A common problem in treating alcoholics is the high dropout rate. Many studies have identified individual factors associated with dropout, eg, poor motivation and previous dropout. We believe the present study reports the first major effort to use multivariate analyses to predict dropout in a large (792), one-year follow-up study of alcoholics, and examines the possibility that medical and nonmedical treatments lead to differential dropout rates. A multiple classification analysis technique showed that treatment variables as opposed to client characteristics were the best predictors of dropout. Patients remaining in treatment were more likely to have a variety of medical interventions, eg, medication and medical assessment, than those who dropped out. Results were similar to studies using other techniques and have interesting implications for the treatment of alcoholics, raising questions about current trends toward nonmedical treatment of alcoholism.

Alcoholism↗